The present invention relates to a device for processing bristle filaments of brushes, in particular tooth brushes, with an abrasive surface. Moreover, the present invention relates to a method of processing bristle filaments of brushes, in particular toothbrushes, in which an abrasive surface is moved relative to the operative ends of the bristle filaments.
The operative ends of the bristle filaments of a brush must be processed from time to time to remove ridges produced during manufacture of the bristle filaments. Moreover, in particular in the case of toothbrushes, the operative ends must be rounded off for protecting the mucous membrane. The aforementioned rounding operation poses problems in particular in cases where the bristles are profiled, i.e. not all of the operative ends of the bristle filaments are positioned in one plane. In particular in the case of toothbrushes, the bristles are provided with very different contours for achieving preferred cleaning effects, which makes the processing of the operative ends difficult and often produces unsatisfactory results.
DE-A-197 28 493 discloses an apparatus and a method for processing portions of a field of bristles of contoured brushes. The device comprises a template for deflecting and pressing away the longer bristle filaments in order to expose the shorter bristle filaments of the array of bristles at their operative ends, whereby they can be processed in a satisfactory manner. In this process the shorter bristle filaments project through openings provided on the template. EP 0 458 999 discloses a device comprising shield elements with inclined portions for deflecting selected bundles of bristles of a field of bristles so as to expose other bundles of bristles of the array of bristles and to process the same with the necessary intensity. The two above-described devices have the drawback that the shield elements and the template, respectively, must positioned in order to deflect the desired bristle filaments or bundle of bristles. This poses problems, in particular, in the case of an array of relatively densely positioned exactly bristles, as is for instance the case with toothbrushes.
An incorrect positioning is bound to have the effect that filaments which are arranged next to the bristle filaments to be deflected are also picked up by the template or the shield elements, whereby they are deprived of a processing operation. The aforementioned filaments will no longer be processed in a subsequent processing step in which the longer bristle filaments are rounded at their operative ends, so that the finished brush includes unprocessed bristle filaments and is thus defective. Moreover, the shield elements or the template obstruct a free wobble length of the bristle filaments to be processed, which length is needed for rounding the filaments in a satisfactory manner. Moreover, great effort is required for performing the above-described method with such a device.
WO 93/12691 discloses a method of producing a contoured brush in which only the bristle bundles whose operative ends are located in one plane are respectively connected to the brush body and rounded off with a conical grinder having a plain abrasive surface. First, the bristle filaments whose operative ends are positioned in the lowermost plane are connected to the brush body and rounded; then the next plane will be treated, etc. This method is very troublesome and, in the final analysis, can only be carried out in an economic way if the position of the operative ends of the bristle filaments is limited to a few planes and the planes are graded in discrete steps. Consequently, the prior method is not suited for producing subsequently rounded bristle filaments in an array of bristles having a continuous contour extension.
It is the object of the present invention to provide an apparatus and a method for efficiently processing the operative ends, in particular of contoured brushes, in an efficient manner.
To achieve the above object, the present invention provides for a device of the above-mentioned type in which the abrasive surface is formed on at least one tooth flank of at least one tooth provided on a rotating circumferential surface and circulating in a rotational direction.
The device according to the invention comprises at least one tooth, preferably a plurality of teeth, whose at least one tooth flank has formed thereon an abrasive surface. The teeth are provided on a rotating circumferential surface, e.g. on the circumferential surface of a drum or a rotating belt. The operative ends of the bristle filamerits are guided relative to the tooth flanks substantially in the longitudinal direction of the tooth flanks in a first direction, and in a second direction perpendicular to the first direction, over the ridge of the tooth or the teeth. The shape and configuration of the teeth allow different contours of the array of bristles can be accommodated. The array of bristles is guided in a direction transverse to the longitudinal extension of the tooth and over the tooth flank comprising the abrasive surface such that all of the operative ends of the bristle filaments can be processed in any plane of the contour. Practical tests have demonstrated that the device of the invention is far superior to conventional grinders that have a plain, abrasive and rotating surface which is substantially guided in wobbling fashion around the operative ends of the bristle filaments so as to round the same, i.e. in particular in the processing of a contoured array of bristles of a brush.
An automatic rounding of the operative ends of the bristle filaments, which are located in different planes, is in particular achieved in that said filaments travel over the tooth flank and sweep over the ridge of the tooth in a direction transverse to the longitudinal extension thereof. The aforementioned relative movement between the operative ends of the bristle filaments and the tooth comprising the abrasive surface can be achieved in that the rotating circumferential surface is axially adjustable and drivable, said movement being performed in axial direction preferably cyclically. In a preferred development, which yields a further constructional simplification, a plurality of teeth are however formed in the manner of a helix, thereby passing into one another on the circumferential surface. With such a development, the plurality of teeth that pass into one another in the form of a helix can be shaped on a cylinder like in the case of a conventional external thread. Alternatively, convolutions of a plurality of teeth extending in parallel with each other may be provided with a predetermined pitch on a circulating belt. Due to the arrangement of the teeth in the manner of a helix, the tooth flanks xe2x80x9ctravelxe2x80x9d in an axial direction by virtue of the rotation of the circumferential surface so that the bristle filaments having different lengths are bound to contact the abrasive tooth flank with their operative ends while sweeping over the ridge, whereby they are rounded.
In an advantagous development of the device of the invention all teeth have an identical cross-sectional profile. The configuration of the saw-tooth profile is simplified by such a design. The profile can e.g. be obtained by xe2x80x9cthreadingxe2x80x9d on the circumferential surface of a cylinder.
To achieve the above object according to the method, the generic method is developed in the present invention by the measures that the bristle filaments are moved in a first direction substantially in parallel with at least one tooth flank comprising the abrasive surface, and in a second direction substantially extending at a right angle to the first direction, over the ridge of at least one tooth. It has been found to be of particular advantage when the relative movement between the bristle filaments and the abrasive surface in the first direction is set to a range between 5 and 30 m/s.